Exemplary aspects of this disclosure relate to systems and apparatus for preventing paper edge ghost in an electrophotographic or xerographic system.
The xerographic imaging process is initiated by charging a charge retentive surface, such as that of a photoconductive member, to a uniform potential. The charge retentive surface is then exposed to a light image of an original document, either directly or via a digital image driven laser. Exposing the charged photoconductor to light selectively discharges areas of the charge retentive surface while allowing other areas to remain unchanged. This creates an electrostatic latent image of the document on the surface of the photoconductive member.
Developer material is then brought into contact with the surface of the photoconductor material to develop the latent image into a visible reproduction. The developer typically includes toner particles with an electrical polarity that is the same as, or that is opposite to, the polarity of the charges remaining on the photoconductive member. The polarity depends on the image profile.
A blank image receiving medium is then brought into contact with the photoreceptor and the toner particles are transferred to the image receiving medium. The toner particles forming the image on the image receiving medium are subsequently heated, thereby permanently fixing the reproduced image to the image receiving medium.
Electrophotographic or xerographic laser printers, scanners, facsimile machines and similar document reproduction devices must be able to maintain proper control over the systems of the image forming apparatus to assure high quality output images.
FIG. 1 shows an exemplary embodiment of an image forming apparatus 100 having a photoreceptor 120. The image forming apparatus 100 may be a xerographic printer or other known or later developed xerographic device.
As shown in FIG. 1, one or more latent images may be generated on the photoreceptor 120, in any well known manner, by controlling one or more of a number of different developer units 150 using controller 110.
In many xerographic machines, where high image quality targets are desired, the photoreceptor is first charged. For example, as shown in FIG. 1, in the direction of movement of the photoreceptor 120, as indicated by the arrows, the photoreceptor 120 is charged to lay a first level of toner onto the photoreceptor. Next, the charge laid is exposed by exposing unit 140. Finally, the toner is developed by developing unit 150. The process continues in the direction of movement of the photoreceptor 120 until all layers of toner are laid, for example, to complete an image-on-image full-color image forming process. Once the full-color image is finished, the completed image is transferred to a sheet of image receiving medium 160. In the transfer process, the sheet of image receiving medium 160 is charged by a corona charge device or a bias transfer roller. The layers of toner are transferred to the sheet of image receiving medium 160 by the application of an electrostatic field of a direction urging the toner to move from the photoreceptor 120 to the sheet of image receiving medium 160. Specifically, ions are placed onto the backside of the sheet of image receiving medium by the corona charging device or the bias transfer roller.
The charging procedure of a charging device is performed to produce a very uniform charge on the photoreceptor. This uniform charge is especially important in the image-on-image type xerographic color machines, as shown in FIG. 1, where the photoreceptor may be covered by multiple layers of toner.